Ferroelectric materials exhibit electric polarization in particular directions and permit the simultaneous, side-by-side presence of regions having differing polarization. Examples are gadolinium molybdate and lead germanate, both having just two directions of polarization which are opposites of each other.
Devices have been proposed whose operation is based on scanning motion of a ferroelectric domain wall in a supported or unsupported layer or film of a ferroelectric material, as described, e.g., in J. M. Geary, "Experimental Ferroelectric Domain Wall Motion Devices", Applied Physics Letters,Vol 32 (1978), pp. 455-457 and in J. M. Geary, "Monolithic Electronic Devices Based on Domain Wall Motion in a Ferroelectric Crystal", Bell System Technical Journal, Vol. 58 (1979), pp. 467-489.
Among ferroelectric devices are, in particular, an analog readout device as disclosed in R. A. Lemons et al., "Analog Read-Only Memory Using Gadolinium Molybdate", Applied Physics Letters,Vol. 33 (1978), pp. 373-375. Operation of this device involves scanning motion of a ferroelectric domain wall past a patterned electrode on a ferroelectric film, the pattern being chosen so as to correspond to a desired electrical waveform as may be suitable to drive, e.g., a loudspeaker or an optical display device. Accordingly, each time a domain wall is made to move past such patterned electrode, the desired electrical signal is reproduced.
Readout of one of a plurality of waveforms may be from a device having side-by-side readout tracks. However, disclosed devices require two electrical leads per track which may be prohibitive if the number of tracks is large. Moreover, if a planar-wall type material such as, e.g., gadolinium molybdate is used, readout of a selected track may be subject to interference from nonselected tracks.
Similarly based on ferroelectric domain wall motion in a ferroelectric film is a device, disclosed in above-identified papers by J. M. Geary, for producing an electrical signal in response to a physical influence on a surface; typically, the influence may be a radiation pattern incident on a sensitive layer which adheres to a ferroelectric film. Such assembly of a ferroelectric film and adhering sensitive layer is between electrodes such that, upon application of a suitable voltage, a ferroelectric domain wall moves in the film. As a result of domain wall motion, an electrical current signal can be sensed in a lead to an electrode, such signal being time-varying in correspondence to the spatial variation of radiation incident on the device.
If scanning of a two-dimensional pattern is desired, scanning may be, e.g., in raster fashion by a plurality of adjacent devices. Alternatively, as disclosed in an above-identified paper by J. M. Geary, a device may incorporate a shift register for positioning a ferroelectric domain in a y-direction adjacent to a track to be scanned in an x-direction. Implementation of such x-y design is based on a ferroelectric material in which ferroelectric domains may have arbitrary shape as, e.g., in lead germanate. On the other hand, in the case of devices based on planar-wall type ferroelectric material, it appears necessary to utilize a multitude of adjacent one-dimensional devices to form a two-dimensional device. This, however, may again result in a potentially prohibitive number of electrical connections to a device.